A service for supplying data including a variety of large-capacity contents using a high-definition moving image, a still image, or a sound to an end user through a wireless communication has been studied. In order to transmit large-volume data of several G (giga) bits at a high speed, a radio communication system that conducts high-speed transmission of several Gbps with the use of a millimeter waveband including a 60 GHz band has been studied.
In the millimeter wave wireless communication system, a wireless PAN (personal area network) standardization work is conducted by IEEE 802.15.3c, for example, a wireless LAN (local area network) standardization work is conducted by IEEE 802.11ad.
For example, in a single carrier communication using the millimeter waveband studied by IEEE 802.11ad, a signal that has been subjected to PSK or QAM modulation is transmitted at a transmission rate of 1.76 G symbol/sec. Because one symbol time is shorter, that is, about 0.57 nsec, data is transmitted at an ultrahigh speed in the millimeter wave wireless communication system. Now, an example in which 60 GHz band is used as the millimeter waveband will be described.
In a transmission device, the above modulated baseband signal is frequency-converted into a 60 GHz band by a radio frequency circuit (RF unit), and transmitted from an antenna.
In a reception device, a signal of the 60 GHz band, which is input from an antenna, is frequency-converted into a baseband signal by a radio frequency circuit (RE unit). As the RF unit, several systems including a superheterodyne system or a direct conversion system have been studied. The direct conversion system mixes a carrier frequency of 60 GHz directly with a modulated signal of the 60 GHz band to convert the signal directly into the baseband signal band.
The RF unit of the direct conversion system is simple in the circuit configuration, thereby leading to a reduction in the number of components and a reduction in the power consumption. However, the RF circuit of the direct conversion system suffers from such a problem that a DC offset occurs in the baseband signal by self-mixing in the RF unit. There has been known that the DC offset requires baseband signal processing, for example, an excess dynamic range for the AD converter, and also affects a GC (Gain Control) circuit and a frequency synchronization circuit.
Also, an error of respective oscillators incorporated into the transmission device and the reception device causes a slight error between the carrier frequency of the transmission device side and the carrier frequency of the reception device side. This results in such a problem that the carrier frequency offset occurs in the reception device. There has been known that the carrier frequency offset fluctuates a phase in a receive signal, and causes the deterioration of a demodulation performance.
In the reception device using a direct conversion in the RF unit, as a technique for correcting the carrier frequency offset, there is a wireless communication apparatus disclosed in for example, Patent Literature 1. In Patent Literature 1, the wireless communication apparatus receives a preamble signal having no DC component, converts the preamble signal into a digital signal by an AD converter, and thereafter removes a DC offset component caused by the direct conversion with the use of a high-pass filter (HPF). The wireless communication apparatus estimates the frequency offset with the use of the preamble signal from which the DC offset component has been removed. Then, the wireless communication apparatus corrects the frequency offset of the subsequent receive signal with the use of a frequency offset estimated result.
Also, in the reception device using the direct conversion in the RF unit, as a technique for correcting the DC offset, there is a receiver disclosed in, for example. Patent Literature 2. In Patent Literature 2, the receiver detects the DC offset from a signal that has been converted into a digital signal by an AD converter, converts the amount of correction into an analog signal by a DA converter, and adds the converted analog signal to an analog signal to be input to the AD converter, to thereby correct the DC offset.